Method for protecting metal surfaces against corrosion in liquid or gaseous media

ABSTRACT

A process useful for protecting metal surfaces against corrosion in is presented involving: (a) forming a corrosion inhibitor having a compound corresponding to formula (I):                    
     where R 1 , R 2  and R 3  independently of one another represent an alkyl or hydroxyalkyl group containing 1 to 4 carbon atoms, an aryl or alkylaryl group or a group corresponding to formula (II):                    
     A −  is an anion, n is the number 2 or 3, p is a number of 1 to 3 and R 5  is an alkyl or alkenyl group containing 7 to 23 carbon atoms and 0, 1, 2 or 3 double bonds, and R 4  is a group corresponding to formula (II) or (III):                    
     where R 1 , R 2  and R 3  are as defined above and Z is a group —(CH 2 ) m — or a group corresponding to formula (IV):                    
      m is an integer of 1 to 6, X is a group NH or an oxygen atom and D is a dimer fatty acid residue containing on average 36 to 54 carbon atoms; (b) combining the corrosion inhibitor with liquid aqueous, liquid non-aqueous or gaseous media; and (c) contacting the corrosion inhibitor with metal. The corrosion inhibitor used in the is biodegradable and shows low aquatic toxicity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. §371 national stage application based onInternational Patent Application No. EP97/06451, filed Nov. 19, 1997.

BACKGROUND OF THE INVENTION

The corrosion of metals in liquid or gaseous media is an age-oldproblem. In the field of geological exploration in particular, the metalsurfaces of the equipment used have to be protected against corrosion,for example under the effect of the mildly acidic or deaerated salineaqueous solutions which are used in the production and processing ofpetroleum and natural gas. Petroleum and natural gas and the wateraccompanying them contain corrosive constituents, for example CO₂ or H₂Sand salts, which lead to serious corrosion of metal surfaces. Inaddition, the working fluids, for example drilling muds, used in thisfield also contribute towards corrosion.

Accordingly, so-called corrosion inhibitors are used to provideprotection against corrosion, being added to the liquids or gases whichcome into contact with the metal surfaces. The corrosion inhibitorseither form a film on the metal surface or reduce the corrosion processby physicochemical reactions on the metal surface (cf. P. H. Ogden,Chemicals in the Oil Industry, The Royal Society of Chemistry, 1991,pages 21-22 and O. Lahodny-{haeck over (S)}arc, Corrosion Inhibition inOil and Gas Drilling and Production Operations, Eur. Fed. Corros., Publ.1994, 11, pages 104-112).

Various substances, normally containing nitrogen, have already beenproposed as corrosion inhibitors (O. Lahodny-{haeck over (S)}arc, pages112-113). Mitzlaff et al. (Werkstoff und Korrosion, 40, 629-634 (1989))describe quaternary ammonium compounds as corrosion inhibitors for theproduction of petroleum and natural gas. Phillips et al. (Proceedings ofthe 8th European Symposium on Corrosion Inhibitors, Suppl. N. 10, 1995,1213-1227) describe certain betaines, for example cocoamidopropylcompounds, for the same purpose. EP 320 769 A2 discloses ethoxylatedquaternized ammonium compounds specifically for use in the w/o emulsionsencountered in the production and processing of petroleum.

More recently, corrosion inhibitors have also had to satisfy morestringent requirements in regard to their biodegradability and aquatictoxicity. EP 651 074 describes N-ethoxyimidazolines substituted in the2-position which not only have a favorable corrosion-inhibiting effect,they also show low aquatic toxicity (EC₅₀ in Skeletonema costatum<1ppm).

Since it is precisely the chemicals used in the production of petroleumand natural gas which are having to meet increasingly more stringentenvironmental compatibility requirements, there is still a need toprotect metal surfaces exposed to corrosive liquid or gaseous mediaagainst corrosion without using substances which have only limitedenvironmental compatibility.

It has now been found that certain quaternized ammonium compounds whichcontain at least one ester group in the molecule have a favorablecorrosion-inhibiting effect, are readily biodegradable and show lowaquatic toxicity.

SUMMARY OF THE INVENTION

The present invention relates to processes for protecting metal surfacesagainst corrosion in liquid aqueous or non-aqueous or gaseous media andto the use of certain quatenized ammonium compounds as corrosioninhibitors.

Accordingly, the present invention relates to a process for protectingmetal surfaces against corrosion in liquid aqueous or non-aqueous orgaseous media, characterized in that compounds corresponding to formula(I):

in which R¹, R² and R³ independently of one another represent an alkylor hydroxyalkyl group containing 1 to 4 carbon atoms, an aryl oralkylaryl group or a group corresponding to formula (II):

A⁻ is an anion, n is the number 2 or 3, p is a number of 1 to 3 and R⁵is an alkyl or alkenyl group containing 7 to 23 carbon atoms and 0, 1, 2or 3 double bonds,

and R⁴ is a group corresponding to formula (II) or (III):

where R¹, R² and R³ are as defined above and Z is a group —(CH₂)_(m)— ora group corresponding to formula (IV):

and m is an integer of 1 to 6, X is a group NH or an oxygen atom and Dis a dimer fatty acid residue containing on average 36 to 54 carbonatoms, are added to the media.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the invention is preferably used to protectmetal surfaces, such as occur in the technical equipment used indrilling operations, i.e. for example in pipelines, valves or deliverytubes, against corrosion in liquid aqueous or non-aqueous or gaseousmedia. The equipment in question is generally made of steel. However,the process according to the invention may also be used to preventcorrosion in other metals, for example aluminium, lead or copper, oralloys containing these metals.

The media to which the metals are exposed may be liquid or gaseous. Ingeological exploration work, the principal gaseous medium encountered isnatural gas. A typical liquid non-aqueous medium is, for example, crudeoil. Typical aqueous media preferably contain between 10 and 90% byweight of water. The water encountered in oil and gas production canhave salt contents from 0.2% to saturation level and, accordingly, canseriously corrode metal surfaces. However, purely aqueous media can alsobe encountered, for example in the drilling of drinking water wells.Another medium often encountered are water/oil mixtures or emulsionsused, for example, as drilling muds which can contain up to 99% byweight of oil. Besides crude oil, the oil phase can also containenvironmentally compatible organic esters, for example of the typedescribed in EP 374 671 A1, EP 374 672 A1 or EP 386 636 A1. In addition,the drilling muds contain suspended clay and other additives which areused to control the properties of the drilling mud.

The compounds corresponding to formula (I) are known and today aremainly used as fabric-softening components or for the antistaticfinishing of fabrics. Examples of compounds corresponding to formula (I)where R⁴ is a group of formula (II) can be found in applicants' WO94/06899 and DE 42 03 489 A1 which disclose diester amine compounds infabric softeners. EP 239 910 A1 also describes fabric softenerscontaining readily biodegradable quaternized mono- and diester aminecompounds. In addition, it is known from the literature that ammoniumcompounds of the type in question are distinguished by readybiodegradability (Hauswirtschaft und Wissenschaft, Vol. 42, No. 2, 1994,pages 72-74 and S. T. Giolano et al., Chemosphere, Vol. 30, No. 6, pages1067-1083, 1995).

Compounds corresponding to formula (I), in which R⁴ is a group offormula (III), are described in DE 195 03 277 C1. These compounds arereadily biodegradable and, by virtue of their softening and antistaticeffect, are used as fiber and textile auxiliaries and in hair cosmetics.However, the corrosion-inhibiting properties of these substances areneither mentioned nor suggested in any of the documents mentioned above.

Compounds corresponding to formula (I) where R⁴ is a group of formula(II) are preferably used in the process according to the invention.These compounds are technically quaternized mono-, di- or trifatty acidamine ester compounds which can be obtained by known synthesis methods.Compounds containing one and preferably two fatty acid ester groups arenormally used. The quatemized compounds may be obtained, for example, byesterification of tertiary mono-, di- or trialkanolamines, preferablytriethanolamine or triisopropanolamine, with fatty acid chlorides andsubsequent quaternization of the esters formed with methyl chloride,benzyl chloride or dimethyl sulfate. Particulars of the production ofthese cationic ester amine compounds can be found, for example in EP 293955 A2 and EP 293 953 A2.

Besides the preferred compounds of formula (I) where R⁴ is a groupcorresponding to formula (II), compounds containing two quaternizednitrogen atoms per molecule corresponding to formula (I), where R⁴ is agroup of formula (III), may also be used. Of these compounds, those inwhich the group Z stands for a dimer fatty acid group of formula (IV)are preferred.

The synthesis of these compounds is carried out, for example, inaccordance with the teaching of DE 195 03 277 C1. To this end, tertiaryamines corresponding to formula (V):

in which R⁶ is an NH₂ or OH group and R¹, R² and m are as defined above,are condensed with dimer fatty acids containing on average 36 to 54 arecondensed with dimer fatty acids containing on average 36 to 54 carbonatoms and the dimer fatty acid esters or amides obtained aresubsequently quatemized with known alkylating agents, for exampledimethyl sulfate or dimethyl carbonate, to form the compounds of formula(I) used in accordance with the invention, in which R⁴ is a groupcorresponding to formula (III) and Z is a group corresponding to formula(IV).

In the context of the invention, dimer fatty acids are understood to beoligomeric fatty acids which may be obtained in known manner by thermalor catalytic oligomerization of unsaturated fatty acids, for exampleoleic acid or erucic acid, or technical fatty acid mixtures with iodinevalues in the range from 45 to 115. In the course of the dimerization,which is an electrocyclicene reaction, two fatty acids or, in smallquantities, even three fatty acids are linked to form an unsaturated,but normally non-aromatic ring system.

In the synthesis of these compounds, N,N-dimethylaminopropyl amine orN,N-dimethylaminopropanol is preferably used as the tertiary amine whileoligomerization products of technical oleic acid are used as preferreddimer fatty acids. The molar ratio of amine to dimer fatty acid ispreferably adjusted to a value of 1:1.5 to 1:2.2 in accordance with theteaching of DE 195 03 277.

Compounds of formula (I), in which R⁴ stands for a group correspondingto formula (III), where Z is a methylene group —(CH₂)_(m)—, preferably apolymethylene group containing 6 carbon atoms, may also be used. Ofthese compounds, those in which both quaternized nitrogen atoms eachcarry two ester groups of formula (II) are preferably used. Thesecompounds are prepared by conventionally reacting an alkylenediamine,preferably hexamethylenediamine, with ethylene oxide in a first step,then esterifying the reaction product with a carboxylic acid and finallyquaternizing the ester with suitable compounds, for example dimethylsulfate.

The alkyl group R⁵ corresponding to formula (II) in the compounds offormula (I) used in the process according to the invention is preferablylinear and contains between 7 and 23 carbon atoms. Groups containingfrom 7 to 21 carbon atoms are preferred. The alkyl group may besaturated or unsaturated. Unsaturated alkyl groups may contain 1, 2 or 3double bonds, but preferably contain only 1 double bond.

A particularly preferred process is one which uses compounds of formula(I) in which the ester groups are obtained by esterification of fattyacid mixtures, preferably palm oil, rapeseed oil or coconut oil fattyacids. Other suitable fatty acids are, for example, caprylic, capric,lauric, myristic, palmitic and stearic acids and unsaturated acids, suchas oleic acid, erucic acid, linoleic acid or linolenic acid, behenicacid or mixtures of these compounds. Compounds in which one of thegroups R¹ to R³ is a hydroxyalkyl group, preferably containing 2 to 4carbon atoms, and/or an aryl or alkylaryl group, more particularlycontaining 6 to 12 carbon atoms, preferably a benzyl group, are alsopreferably used.

Another preferred embodiment of the process according to the inventionis characterized by the use of compounds corresponding to formula (I) inwhich one or more of the substituents R¹, R² or R³ is/are also a groupcorresponding to formula (II).

The anions A⁻ of the compounds corresponding to formula (I) used in theprocess according to the invention are determined by the quatemizingagent used in the synthesis, such as methyl chloride, benzyl chloride ordimethyl sulfate. The anions are preferably selected from the group ofhalides, methosulfate and methophosphate.

The compounds corresponding to formula (I) may be used in the processaccording to the invention by addition to the medium to be treated ineffective quantities. Mixtures of compounds corresponding to formula (I)or mixtures with other known inhibitors, for example N-alkyl betaines,N-alkyl imidazolines, polyalkoxylated amines, amides and imidazolines orphosphoric acid esters, may also be used. The process is preferablycarried out by adding the compounds corresponding to formula (I) in suchquantities that their concentration, based on the total quantity ofmedium, is between 5 and 1,000 ppm.

Processes in which the compounds of formula (I) are used in the form ofaqueous solutions are preferred. These solutions contain the compoundsof formula (I) in quantities of preferably 5 to 50% by weight and, morepreferably, 10 to 30% by weight, based on the total weight of thesolutions. The solutions may also contain alcohols, preferably C₁₋₆alcohols, such as isopropanol, ethylene glycol or propylene glycol, ormixtures thereof in quantities of 5 to 30% by weight, based on thequantity of the aqueous solutions.

Besides the ingredients already mentioned, the aqueous solutions mayalso contain other additives, including for example emulsifiers, such asfatty amines or dimer or trimer fatty acids, and H₂S or O₂ scavengers,such as sodium thiosulfate or sodium hydrogen sulfite. These additivesare added to the solutions in typical quantities, i.e. in quantities of1 to 10% by weight.

In another preferred embodiment of the process according to theinvention, the compounds corresponding to formula (I) are used in theform of a solution in a non-aqueous solvent selected from aliphatic oraromatic hydrocarbons liquid at room temperature, the solutionscontaining the compounds of formula (I) in quantities of 5 to 50% byweight and preferably in quantities of 10 to 30% by weight.

Suitable hydrocarbons are, for example, spirit, paraffins liquid at roomtemperature or aromatic hydrocarbons, such as toluene, xylene or diethylbenzene, and mixtures of these compounds.

It has proved to be of advantage to use the non-aqueous solvents inadmixture with short-chain C₁₋₈ alcohols in the process according to theinvention, the ratio by weight of non-aqueous solvent to alcohol beingfrom 1:10 to 10:1 and, more particularly, from 4:1 to 1:4. Suitablealcohols are, for example, ethanol, propanol, isopropanol,2-ethylhexanol, or glycols, for example ethylene or butylene glycol andmixtures thereof. However, the compounds of formula (I) may also be usedin the form of solutions in alcohols. In addition, solutions of thecompounds (I) in non-aqueous solvents may contain other suitableadditives, for example H₂S or O₂ scavengers.

If the process according to the invention is used to protect metalsexposed to gaseous media, the compounds of formula (I) in the form ofaqueous or non-aqueous solutions are sprayed as an aerosol in thegaseous medium.

The present invention also relates to the use of compounds correspondingto formula (I) as corrosion inhibitors for metals in liquid aqueous ornon-aqueous or gaseous media.

The use according to the invention is by no means confined to oil or gasproduction (for example as an additive to drilling muds or as acorrosion inhibitor for pipelines and other pipes), instead thecompounds corresponding to formula (I) are generally suitable for use ascorrosion inhibitors for metal surfaces, preferably steel surfaces.

EXAMPLES Example 1

The corrosion-inhibiting properties were determined by a so-called wheeltest. In this coupon test, the erosion caused by the corrosion ofinhibited systems is compared with the erosion occurring innon-inhibited systems.

To this end, steel coupons (Mild Steel 1018, sand-blasted) weredegreased with acetone and weighed, subsequently immersed in a corrosivemedium and stored therein for 72 hours at 60° C. while turning (60r.p.m.). The corrosive medium used was a mixture of a salt-containingaqueous phase (5% by weight NaCl, 0.5% by weight acetic acid) and spirit(boiling range at normal pressure 145-200° C.), the mixture beingsaturated with CO₂ and H₂S. The mixing ratio (v/v) of water to spiritwas 50:50.

The inhibiting substances were used in the form of a 30% by weightaqueous solution. The concentration in each case was 30 ppm (based onthe quantity of corrosive medium).

The coupons were then washed with an acetone/isopropanol mixture (50:50,v/v), dried and reweighed. The protective effect compared with couponsstored without corrosion control was determined from the difference inweight of the coupons before and after the treatment in the corrosivemedium. A weight loss of 0 mg represents a protective effect of 100%.

Table 1 below shows these values for inhibitors 1 to 5 according to theinvention and, for comparison, the value of a conventional betaineinhibitor. Inhibitors 1 to 5 according to the invention clearly show asignificantly better protective effect.

TABLE 1 Protective effect Inhibitor (in %) 1 71 2 77 3 89 4 87 5 85 C 37

Composition of the Inhibitors:

1: Methyl-N,N-bis-(coco-oxyethyl)-N-(2-hydroxyethyl)ammoniummethosulfate

2: N,N,N-trimethyl-N-(coco-oxyethyl)ammonium methosulfate

3: N,N-dimethyl-N-benzyl-N-(coco-oxyethyl)ammonium chloride

4: N,N,N-trimethyl-N-(palmoxyethyl)ammonium methosulfate

5: N,N-dimethyl-N-benzyl-N-(palmoxyethyl)ammonium chloride

V: N,N-dimethyl-N-(cocoamidopropyl)-N-acetyl betaine

Examples 2

Besides the pure inhibitors, mixtures containing additional additivesneeded, for example, in the petroleum industry were also investigated.The mixtures in question are ready-to-use formulations for use undertypical conditions, for example during drilling or in the production ofpetroleum or natural gas. The mixtures were subjected to theabove-described wheel test in which the corrosive medium was the samemixture as in Example 1, except that the water-to-spirit ratio (v/v) was10:90 (for the results, see Table 2). The mixtures contained 20% byweight of inhibitor, 10% by weight of isopropanol as co-solvent, 2% byweight of a cocofatty amine reacted with 12 moles of ethylene oxide, 2%by weight of trimer tall oil fatty acid, 2% by weight of sodiumthiosulfate as H₂S scavenger and, for the rest, water. The inhibitorsused were compounds 3 and 4 mentioned above.

TABLE 2 Protective effect Inhibitor (in %) 3 89 4 87

Example 3

Inhibitors 2 to 5 were dissolved in a solvent mixture of 40% by weightof isopropanol and 60% by weight of aromatic hydrocarbons (Solvesso150®, a product of Exxon). The solutions each contained 25% by weight ofthe inhibitor. They were subjected to the above-described wheel test(concentration of the inhibitors 10 ppm, based on the corrosive medium):

TABLE 3 Protective effect Inhibitor (in %) 2 88 3 89 4 90 5 86

Example 4

Corrosion inhibitors 6 and 7 according to the invention were subjectedto the wheel test under the conditions of Example 3. The ratio by volumeof water to organic phase was 90:10. The organic phase consisted orequal parts by volume of isopropanol and Solvesso® 150.

Inhibitor 6 was prepared by initially reacting 436 g ofhexamethylenediamine (3.8 moles) with 995 g of ethylene oxide (22.6moles) in the absence of a catalyst at 120-130° C./1 bar pressure.

410 g (1.3 moles) of this ethoxylated hexamethylenediamine wereesterified with 590 g of stearic acid (2.1 moles) and 1.5 g ofphosphinic acid at 170° C./0.4 bar pressure until the acid value of theproduct had fallen to a value below 5.795 g of the ester were then mixedwith 500 g of isopropyl alcohol and heated to 60° C., after which 213 g(2 moles) of dimethyl sulfate were added for quaternization. The mixturewas then heated for 4 hours to 80° C., after which the product wasobtained as a light yellow paste.

Inhibitor 7 is a commercially available dimer fatty acid amidoamine(Empol 1014, a product of Henkel KGaA) which has been quaternized withdimethyl sulfate.

The results are set out in Table 4:

TABLE 4 Protective effect Inhibitor (in %) 6 92 7 93

The results of these tests show that even the ready-to-use mixturesretain their favorable protective effect.

What is claimed is:
 1. A process for protecting a metal surface againstcorrosion, the process comprising: (a) providing a metal surface to beprotected against corrosion; (b) providing a compound of the generalformula (I):

wherein R¹, R² and R³ each independently represent an alkyl orhydroxyalkyl group having from 1 to 4 carbon atoms, an aryl or alkylarylgroup or a group corresponding to the general formula (II):

wherein A⁻ represents an anion, n is equal to 2 or 3, p is a number from1 to 3 and R⁵ represents an alkyl or alkenyl group having from 7 to 23carbon atoms and up to 3 double bonds, and R⁴ represents a groupcorresponding to the general formula (II) or (III):

wherein R¹, R² and R³ are as defined above and Z represents —(CH₂)_(m)—or a group corresponding to the general formula (IV):

 wherein m is an integer of from 1 to 6, each X independently representsan —NH— group or an oxygen atom and D represents a dimer fatty acidresidue containing an average number of carbon atoms of from 36 to 54;and (c) contacting the metal surface with a corrosion-inhibitingeffective amount of the compound.
 2. The process according to claim 1,wherein A⁻ represents an anion selected from the group consisting ofhalides, methosulfate and methophosphate.
 3. The process according toclaim 1, wherein (c) contacting the metal surface with thecorrosion-inhibiting effective amount of the compound comprises: (i)combining the compound with a medium, and (ii) contacting the metalsurface with the medium containing the compound; wherein the medium isselected from the group consisting of liquid aqueous media, liquidnon-aqueous media, and gaseous media.
 4. The process according to claim3, wherein the compound is combined with the medium in an amount of from5 to 1000 parts per million parts of the medium.
 5. The processaccording to claim 1, wherein the compound is provided as an aqueoussolution. 6.The process according to claim 5, wherein the aqueoussolution comprises from 5 to 50% by weight of the compound.
 7. Theprocess according to claim 5, wherein the aqueous solution comprisesfrom 10 to 30% by weight of the compound.
 8. The process according toclaim 5, wherein the aqueous solution further comprises from 5 to 30% byweight of isopropanol, ethylene glycol, propylene glycol or mixturesthereof.
 9. The process according to claim 1, wherein the compound isprovided as a non-aqueous solution containing one or more hydrocarbonswhich are liquid at room temperature.
 10. The process according to claim9, wherein the non-aqueous solution comprises from 5 to 50% by weight ofthe compound.
 11. The process according to claim 9, wherein thenon-aqueous solution comprises from 10 to 30% by weight of the compound.12. The process according to claim 9, wherein the non-aqueous solutionfurther comprises a C₁₋₈ alcohol.
 13. The process according to claim 12,wherein the one or more hydrocarbons and the alcohol are present in aweight ratio of from 1:10 to 10:1.
 14. The process according to claim12, wherein the one or more hydrocarbons and the alcohol are present ina weight ratio of from 1:4 to 4:1.
 15. The process according to claim 1,wherein the compound contains an ester group obtained by theesterification of a member selected from the group consisting of palmoil, rapeseed oil, and coconut fatty acids.
 16. The process according toclaim 3, wherein the compound is provided as an aerosol and is sprayedinto a gaseous media prior to contact with the metal surface.